Concrete retaining walls, building walls and other walls are sometimes covered with wall stones, tiles and other decorative plates for decoration and other purposes. As a typical method of placing decorative plates, it is known one in which decorative plates are tentatively fixed on a surface of a form for molding a concrete product, and concrete is poured into the form with this condition, whereby placing of the decorative plates are carried out at the same time when the concrete is hardened.
As a mechanism for tentatively fixing decorative plates on a form in the above method, there is known one that uses bolt and nut to tentatively fix the decorative plates on the surface of a form, wherein the bolt is removed after the concrete is hardened, and the nut is left as it is embedded in the concrete. For example, JP-A 62-59760 discloses such a mechanism for tentatively fixing a decorative plate.
The conventional mechanism for tentatively fixing a decorative plate, however, has problems as follows.
First, such decorative plates as a stone material and the like have sometimes a front surface which is a finished flat one, but have a back surface left uneven as it is when quarried. No problem may occur when bolt and nut or other tentative fixing means is used to tentatively fix a decorative plate one by one on a form panel. However, when a single tentative fixing means is used to tentatively fix four decorative plates on a form panel at one time as disclosed in the above-mentioned patent publication for the purpose that tentative fixing operation is carried out in a short time, there is a possibility that the four decorative plates are not properly fixed on the form panel because each decorative plates has a different thickness. If tentative fixing of the decorative plate on the form panel is not carried out securely, the decorative plate may fall off the form panel due to forces and vibration applied to the decorative plate when concrete is poured.
Second, when a bolt constituting the tentative fixing mechanism is removed after concrete is hardened, since the thread portion of the bolt is embedded in the concrete, the bolt cannot easily be removed, which is a problem.
Third, a decorative plate must be placed appropriately at a predetermined position when it is tentatively fixed on a form panel. If the decorative plate cannot be positioned effectively and easily, efficiency of its placing operation is degraged, which is not appropriate.